1. Field of the Invention
The present invention relates to a graft copolymer of a syndiotactic styrene/para-alkylstyrene copolymer.
2. Description of the Prior Art
Syndiotactic polystyrene (sPS) is very useful in many commercial applications. However, it suffers from a major deficiency: poor adhesion to other materials (for example, to the copper of PC boards). In addition, sPS has poor compatibility with other functional polymers. Therefore, there is a need to improve the physical properties of the conventional syndiotactic polystyrene.
Chung et al. in U.S. Pat. No. 5,543,484 have disclosed a functionalized x-olefin/para-alkylstyrene copolymer. First, (xcex1-olefin and para-alkylstyrene are copolymerized. The incorporation of p-alkylstyrene into the xcex1-olefin polymer results in the generation of benzylic protons, which are readily available for many chemical reactions, thereby introducing functional groups at the benzylic position under mild reaction conditions. Then, the olefin/p-alkylstyrene copolymer is functionalized by the functionalization of benzylic protons in p-alkylstyrene units. Such functionalization leads to improvement in the physical properties of the original olefin polymers.
Powers et al. in U.S. Pat. No. 5,548,029 has disclosed graft copolymers of para-alkylstyrene/isoolefin. In a similar manner, isoolefin and para-alkylstyrene are copolymerized, and then the p-alkylstyrene/isoolefin copolymer is functionalized by the functionalization of benzylic protons in p-alkylstyrene units. By such functionalization, the physical properties of the isoolefin polymer can be improved.
In Powers et al., to improve compatibility of the isoolefin/p-alkylstyrene copolymer with other polymers (for example, with thermoplastic polymers), grafting technique can also be used. That is, a thermoplastic polymer moiety is grafted onto the functional copolymer. Moreover, such a graft copolymer can also serve as a compatibilizer to compatibilize polymer blends.
To date, no one has ever provided a graft copolymer of syndiotactic styrene/para-alkylstyrene copolymers.
The object of the present invention is to solve the above-mentioned problems and to provide a graft copolymer of a syndiotactic styrene/para-alkylstyrene copolymer. The compatibility of the graft copolymer of syndiotactic styrene/para-alkylstyrene copolymer of the present invention with other polymers is improved over a syndiotactic styrene polymer. Moreover, the graft copolymer of a syndiotactic styrene/para-alkylstyrene copolymer of the present invention can serve as a compatibilizer for a polymer blend so as to improve the compatibility of the polymer blend with other polymers, and increase the impact resistance and elongation of the polymer blend, while the physical properties of the original polymers in the polymer blend can still be maintained.
To achieve the above-mentioned object, the graft copolymer of a syndiotactic styrene/para-alkylstyrene copolymer of the present invention has the formula of
wherein
R1 and R2 are independently selected from the group consisting of hydrogen, alkyl, and primary and secondary haloalkyl,
X is a functional group selected from a group containing halogen, oxygen, sulfur, silicon, nitrogen, carbon, phosphorus, and mixtures thereof,
Y is an atactic polymer moiety,
a ranges from 10 to 30000,
b ranges from 0 to 30000,
c ranges from 0 to 30000, and
d ranges from 1 to 30000.
The present invention is the first time a graft-from copolymer of a syndiotactic styrene/para-alkylstyrene copolymer has been successfully provided.
The graft-from copolymer of a syndiotactic styrene/para-alkylstyrene copolymer has the formula of
wherein R1 and R2 are independently selected from the group consisting of hydrogen, alkyl, and primary and secondary haloalkyl.
X is a functional group selected from a group containing halogen, oxygen, sulfur, silicon, nitrogen, carbon, phosphorus, and mixtures thereof. Preferably, R1 and R2 are independently selected from the group consisting of hydrogen, C1 to C5 alkyl, and C1 to C5 primary and secondary haloalkyl.
Y is an atactic polymer moiety.
a ranges from 10 to 30000, b ranges from 0 to 30000, c ranges from 0 to 30000, and d ranges from 1 to 30000.
Preferably, the copolymer has a number average molecular weight of at least 1000.
The general process for preparing the graft copolymer of a syndiotactic styrene/para-alkylstyrene copolymer of the present invention will be described below.
The grafting techniques can be classified into xe2x80x9cgraft-fromxe2x80x9d and xe2x80x9cgraft-onxe2x80x9d. Graft-from technique involves the reaction of a syndiotactic styrene/p-alkylstyrene copolymer and a monomer via anionic polymerization, cationic polymerization, anionic or cationic ring-open polymerization, or free radical polymerization. A xe2x80x9cgraft-fromxe2x80x9d anionic polymerization is as follows: 
The reaction of a functionalized (such as brominated) syndiotactic styrene/p-alkylstyrene with a monomer via cationic polymerization is as follows: 
The reaction of a functionalized (such as brominated) syndiotactic styrene/p-alkylstyrene with a monomer via free radical polymerization is as follows: 
The xe2x80x9cgraft-onxe2x80x9d technique involves the reaction of a functionalized syndiotactic styrene/p-alkylstyrene copolymer and a polymer which can react with the functional group of such a functionalized syndiotactic styrene/p-alkylstyrene copolymer, such that the polymer bonds to the functionalized syndiotactic styrene/p-alkylstyrene copolymer and grafting is achieved.
Therefore, Y in formula (I) is selected from the group consisting of polymers and copolymers of anionically polymerizable monomers, cationically polymerizable monomers, anionically and cationically ring-openable monomers, and free radical polymerizable monomers.
Representative examples of the anionically polymerizable monomers include conjugated dienes, vinyl aromatic compounds, vinyl unsaturated amides, acenaphthylene, 9-acrylcarbazole, acrylonitrile, methacrylonitrile, organic isocyanates, acrylates, methacrylates, alkyl acrylates, alkyl methacrylates, glycidyl methacrylates, vinyl pyridines, and mixtures thereof.
Representative examples of the cationically polymerizable monomers include vinyl aromatic compounds, vinyl ethers, N-vinylcarbazole, isobutene, and mixtures thereof.
Representative examples of the ring-openable monomers include cyclic ethers, sulfides, lactones, lactams, N-carboxyanhydrides, cyclic anhydrides, and mixtures thereof.
Representative examples of the free radical polymerizable monomers include vinyl aromatic compounds, conjugated dienes, acrylates, methacrylates, alkyl acrylates, alkyl methacrylates, vinyl acetates, and mixtures thereof.
As a result, after further grafting (e.g., graft-from or graft-on), the syndiotactic styrene/para-alkylstryene copolymer of the present invention has a grafted side chain (Y) that is an atactic polymer, rather than a syndiotatic polymer.
The general process for preparing the functionalized syndiotactic styrene/para-alkylstyrene copolymer of the present invention will be described below.
We take the reaction of styrene and para-methylstyrene monomers as an example. First, the two monomers are copolymerized by using a metallocene as a catalyst. The catalyst system may also include an activating cocatalyst such as methyl aluminoxane (MAO). 
wherein each x and y is the molar ratio of the respective monomer and x+y=100.
Suitable metallocene catalysts have a delocalized xcfx80-bonded moiety with a constrained geometry. The catalysts may be further described as a metal coordination complex comprising a metal of Groups IVB-VIB of the Periodic Table of the elements and a delocalized xcfx80-bonded moiety with a constrained geometry. Some of them have been taught in U.S. Pat. Nos. 4,542,199; 4,530,914; 4,665,047; 4,752,597; 5,026,798; and 5,272,236. Preferred catalyst complexes include zirconocene and titanocene coordination compounds with single or double cyclopentadienyl derivatives which form the constrained ligand geometry.
The activating cocatalyst can be methyl aluminoxane (MAO), a trialkyl aluminum, a dialkyl aluminum, a salt of an inert and non-coordinating anion, or a mixture thereof.
The trialkyl aluminum can be selected from the group consisting of trimethyl aluminum, triethyl aluminum, tripropyl aluminum, trisopropyl aluminum, tributyl aluminum, and truisobutyl aluminum (TIBA).
The inert and non-coordinating anion can be a borate. Borates that are suitable for use in the present invention include N,N-dimethyl anilinium tetrakis(pentafluorophenyl)borate, triphenyl carbenium tetrakis(pentafluorophenyl)borate, trimethyl ammonium tetrakis(pentafluorophenyl)borate, ferrocenium tetrakis(pentafluorophenyl)borate, dimethyl ferrocenium tetrakis(pentafluorophenyl)borate, and silver tetrakis(pentafluorophenyl)borate.
Preferably, the activating cocatalyst is methyl aluminoxane, or a mixture of a trialkyl aluminum and a borate.
Suitable diluents for the monomers, catalyst components and polymeric reaction products include the general group of aliphatic and aromatic hydrocarbons, used singly or in a mixture, such as propane, butane, pentane, cyclopentane, hexane, toluene, heptane, isooctane, etc.
In general, the polymerization reaction of the present invention is carried out by mixing styrene and p-methylstyrene in the presence of the catalyst and diluent in a copolymerization reactor, with thorough mixing at a temperature between 0xc2x0 C. to 100xc2x0 C. The polymerization may be carried out in an inert gas atmosphere and the substantial absence of moisture.
The advantage of the styrene/p-methylstyrene is that the benzylic protons in the p-methylstyrene unit can be easily converted to various functional groups, such as xe2x80x94COOH, xe2x80x94OH, xe2x80x94NH2, xe2x80x94Cl, xe2x80x94Br, xe2x80x94M, COOM (M=metal, e.g. Li, Na, K and Ca), under mild reaction conditions. Most functionalization reactions of benzylic protons in organic compounds can be applied to those of benzylic protons in p-methylstyrene.
The following equations, involving (but not limited to) bromination and carboxylation reactions of the syndiotactic styrene/p-methylstyrene copolymer are used to illustrate the functionalization reactions of benzylic protons in the syndiotactic styrene/p-methylstyrene copolymer. 
Among the functionalization reactions of the benzylic protons in the syndiotactic styrene/p-alkylstyrene copolymer, halogenation and metallation are the most important. The halogenation reaction results in a benzylic halogen, which constitutes a very active electrophile that can be converted to various functionalities via nucleophilic substitution reactions. The metallation reaction results in a benzylic anion in the p-alkylstyrene unit, which can be converted to many other functionalities. In fact, halogenated and metallated syndiotactic styrene/p-alkylstyrene copolymers significantly broaden the scope of achievable function groups to include almost all the desirable organic functional groups.
Therefore, via the direct reaction of the unfunctionalized syndiotactic styrene/p-alkylstyrene, or via the reaction of the halogenated or metallated syndiotactic styrene/p-alkylstyrene, the functional group X on formula (I) may be a group containing halogen, metal, oxygen, sulfur, silicon, nitrogen, carbon, phosphorus, or combinations thereof. The functional groups X on the benzylic position have been taught in U.S. Pat. Nos. 5,543,484 (Chung, et al.); 5,548,029 (Powers et al.); and 5,162,445 (Powers, et al.)
Representative examples of the functional group X containing a metal include alkali and alkaline earth metals.
Examples of the functional group X containing oxygen, which results in attachment of xe2x80x94Oxe2x80x94 to the benzylic position from which the halide ion is displaced, include alkoxides, phenoxides and carboxylates.
Examples of the functional group X containing sulfur, which results in attachment of xe2x80x94Sxe2x80x94 to the benzylic position from which the halide ion is displaced, include thiolates, thiophenolates, thioethers, thiocarboxylates, dithiocarboxylates, thioureas, dithiocarbamates, xanthates and thiocyanates.
Examples of the functional group X containing silicon, which results in attachment of xe2x80x94Sixe2x80x94 to the benzylic position from which the halide ion is displaced, include silanes and halosilanes.
Examples of the functional group X containing carbon, which results in attachment of xe2x80x94Cxe2x80x94 to the benzylic position from which the halide ion is displaced, include malonates, cyanides, and CR33 wherein each R3 is an organic group.
Examples of the functional group X containing nitrogen, which results in attachment of xe2x80x94Nxe2x80x94 to the benzylic position from which the halide ion is displaced, include amides, amines, carbazoles, phthalimides, pyridine, maleimide and cyanates.
Examples of the functional group X containing phosphorus, which results in attachment of xe2x80x94Pxe2x80x94 to the benzylic position from which the halide ion is displaced, include phosphines.